U.S. patent application number 14/759976 was filed with the patent office on 2015-12-10 for polyurethane dispersion based synthetic leathers.
The applicant listed for this patent is ROHM AND HAAS COMPANY. Invention is credited to Jiansheng Feng, Weichao Gu, Ning Kang, Qian Shen, Yunfei Yan, Chao Zhang, Hongliang Zhang.
Application Number | 20150354133 14/759976 |
Document ID | / |
Family ID | 51166505 |
Filed Date | 2015-12-10 |
United States Patent
Application |
20150354133 |
Kind Code |
A1 |
Yan; Yunfei ; et
al. |
December 10, 2015 |
POLYURETHANE DISPERSION BASED SYNTHETIC LEATHERS
Abstract
A multilayer structure including (a) a fabric, (b) a
polyurethane foam containing a plurality of cells defined therein,
wherein the foam contains at least one surfactant, and (c) a skin
layer, wherein the skin layer comprises a wetting agent and an
acrylic polymer having a glass transition temperature of -20 degree
Celsius or less, and the foam resides between the fabric and the
skin layer; and the process of preparing the multilayer
structure.
Inventors: |
Yan; Yunfei; (Shanghai,
CN) ; Kang; Ning; (Shandong, CN) ; Feng;
Jiansheng; (Shanghai, CN) ; Shen; Qian;
(Shanghai, CN) ; Zhang; Chao; (Shanghai, CN)
; Gu; Weichao; (Shanghai, CN) ; Zhang;
Hongliang; (Shanghai, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ROHM AND HAAS COMPANY |
Philadelphia |
PA |
US |
|
|
Family ID: |
51166505 |
Appl. No.: |
14/759976 |
Filed: |
January 11, 2013 |
PCT Filed: |
January 11, 2013 |
PCT NO: |
PCT/CN2013/070353 |
371 Date: |
July 9, 2015 |
Current U.S.
Class: |
428/160 ;
156/247; 428/319.3 |
Current CPC
Class: |
C09D 175/06 20130101;
D06N 3/0059 20130101; B32B 27/308 20130101; D06N 3/047 20130101;
D06N 3/0097 20130101; D06N 3/042 20130101; Y10T 428/24512 20150115;
B32B 5/245 20130101; B32B 2266/0278 20130101; D06N 2211/28
20130101; D06N 3/183 20130101; B32B 27/065 20130101; D06N 3/14
20130101; Y10T 428/249991 20150401 |
International
Class: |
D06N 3/14 20060101
D06N003/14; D06N 3/18 20060101 D06N003/18; D06N 3/04 20060101
D06N003/04; C09D 175/06 20060101 C09D175/06; D06N 3/00 20060101
D06N003/00 |
Claims
1. A multilayer structure comprising: (a) a fabric, (b) a
polyurethane foam containing a plurality of cells defined therein
and at least one surfactant, and (c) a skin layer, wherein the skin
layer comprises a wetting agent and an acrylic polymer having a
glass transition temperature of -20 degree Celsius or less, and the
foam resides between the fabric and the skin layer.
2. The multilayer structure of claim 1, wherein the wetting agent
is selected from a silicon surfactant, a fluorine surfactant or
mixtures thereof.
3. The multilayer structure claim 1 further comprising (d) a
finishing layer, wherein the skin layer resides between the
finishing layer and the foam, and the finishing layer comprises a
wetting agent, a crosslinked acrylic polymer wherein the acrylic
polymer has a glass transition temperature of -20 degree Celsius or
less.
4. The multilayer structure of claim 3, wherein the skin layer or,
if present, the finishing layer is embossed.
5. The multilayer structure of claim 3, wherein the multilayer
structure is free of organic solvent.
6. The multilayer structure of claim 3 further comprising (e) a
release paper, wherein the skin layer resides between the foam and
the release paper, or if present, the finishing layer resides
between the skin layer and the release paper.
7. A process for preparing the multilayer structure of claim 1,
comprising the steps of: (i) providing a polyurethane foam coated
on a fabric, wherein the foam comprises a plurality of cells
defined therein, and at least one surfactant, (ii) providing a
release paper, (iii) providing a skin layer, (iv) attaching the
foam to the release paper with the skin layer therebetween to form
a release sheet, so that the foam resides between the skin layer
and the fabric; wherein the skin layer comprises a wetting agent
and an acrylic polymer having a glass transition temperature of -20
degree Celsius or less, and (v) removing the release paper from the
release sheet.
8. The process of claim 7, wherein the release paper is an embossed
release paper.
9. The process of claim 7, wherein the polyurethane foam is
obtained by the steps of: (I) frothing a composition comprising an
aqueous polyurethane and a surfactant, (II) applying the frothed
composition to a fabric to form a coated fabric, and (III) drying
the coated fabric, thus forming a polyurethane foam coated on the
fabric.
10. The process of claim 7, wherein the release sheet is obtained
by applying an aqueous skin coating composition to the release
paper, drying the skin coating composition to form the skin layer,
contacting the foam to the release paper with the skin layer
therebetween, and applying pressure to the resultant sheet; wherein
the skin coating composition comprises the wetting agent and the
acrylic polymer.
11. The process of claim 10 further comprising the steps of:
applying an aqueous finishing composition to the release paper in
step (ii), or applying the aqueous finishing composition to the
skin layer of the multilayer structure obtained after step (v);
then drying the aqueous finishing composition to form a finishing
layer; so that the skin layer resides between the foam and the
finishing layer, wherein the aqueous finishing composition
comprises a wetting agent, a crosslinking agent, and an acrylic
polymer, wherein the acrylic polymer has a glass transition
temperature of -20 degree Celsius or less.
12. The process of claim 10, wherein the skin coating composition
contains from 10 weight percent to 95 weight percent of the acrylic
polymer, where weight percentage is based on the solids weight of
the skin coating composition.
13. The process of claim 11, wherein the skin coating composition
or the finishing composition further comprises an aqueous
polyurethane dispersion, a silicon resin, a matting agent or
combinations thereof.
14. The process of claim 11, wherein drying the skin coating
composition or the finishing composition is conducted for 0.5 to 3
minutes at a temperature of from 90 to 150 degree Celsius.
15. The process of claim 11, wherein the skin layer or the
finishing layer has a thickness of from 5 microns to 500 microns.
Description
FIELD
[0001] The present invention relates to a synthetic leather and a
process for preparing thereof.
BACKGROUND
[0002] Polyurethane (PU) synthetic leathers generally comprise a
fabric, a PU skin layer and a PU foam (also known as a poromeric
layer) sandwiched between the fabric and the skin layer. The foam
mainly contributes to softness and hand-feel of the PU synthetic
leather. The skin layer can provide additional features including
patterns, color, gloss, and abrasion resistance.
[0003] Currently, most PU synthetic leathers are made using
volatile organic solvents such as dimethylformamide (DMF),
methylethyl ketone (MEK) and toluene. These solvent-based systems
are less environmentally friendly and less healthy than aqueous
systems. Therefore, aqueous systems are more desirable.
[0004] Attempts have been made to minimize the use of volatile
organic solvents in the manufacturing of PU synthetic leather.
W02004061198A1 discloses a method for preparing a synthetic leather
including impregnating or coating a non-woven or woven textile with
an aqueous polyurethane dispersion (also known as PUD) to form a
poromeric layer. The prior art does not disclose how to prepare
synthetic leathers comprising an outer layer that is also made from
aqueous compositions.
[0005] In preparing solvent-based PU synthetic leathers, a release
paper process is one widely used approach. The release paper
process typically comprises the steps of: (1) providing a PU foam
coated on a fabric, which is made using an organic solvent; (2)
applying a solvent-based PU resin paste to a release paper to form
a skin layer; (3) attaching the foam to the release paper with the
skin layer therebetween to form a multilayer sheet; (4) peeling off
the release paper from the multilayer sheet to obtain a synthetic
leather with a surface that has a profile corresponding to that of
the release paper. When an embossed release paper is used, the
resultant PU synthetic leathers have an embossed surface, which is
desirable for many applications for advantageous visual
appearance.
[0006] Compared to solvent-based compositions used to form a skin
layer, aqueous compositions usually have poorer coatability on
release paper because release paper is hydrophobic. As a result,
synthetic leathers made thereform may have a flawed surface, for
example, holes or cracks on the surface. Thus, it is challenging to
use the release paper process to prepare synthetic leathers which
have both the foam and the skin layer made from aqueous
compositions.
[0007] Moreover, replacing solvent-based compositions with aqueous
compositions may have undesirable effects on mechanical properties
of synthetic leathers. Synthetic leathers made from aqueous
compositions contain surfactants and can be free of organic
solvents. Both migration of surfactants to the interface of
different layers, and an absence of organic solvents that can cause
the molecules of polymer layers to interpenetrate may cause the
synthetic leather to have lower interlayer adhesion strength than
solvent-based PU synthetic leathers. In addition, aqueous
compositions generally form films with lower film strength than
that of solvent-based compositions, which may compromise bally flex
property and/or abrasion resistance of the resultant synthetic
leathers.
[0008] The PU synthetic leather industry requires synthetic
leathers having certain adhesion strength and bally flex property
to meet national and/or industry standards. The adhesion strength,
that is, interlayer adhesion strength between any two adjacent
layers of the synthetic leather, should be 1,000 gram per
centimeter of sample width (g/cm) or more as measured by Method
SLF11 adopted by the Society of Leather Technologists and Chemists.
To withstand frequent bending during applications, PU synthetic
leathers also need to pass 10,000 times of bally flex test as
measured by China's GB/T 8949-1995. It is also desirable that PU
synthetic leathers have sufficient abrasion resistance for use in
some applications such as in automotives.
[0009] Therefore, it is desirable to provide a process for
preparing a multilayer structure suitable for use as a synthetic
leather, which is carried out free from organic solvents. It is
desirable that such multilayer structure comprises a PU foam and a
skin layer both made from aqueous compositions, and can be free
from surface flaws. At the same time, it is desirable for such
multilayer structure to have the previously described adhesion
strength and bally flex property to meet national and/or industry
standards. Moreover, it is desirable to provide a multilayer
structure having an embossed surface while still having the
previously described adhesion strength and bally flex property.
BRIEF SUMMARY
[0010] The present invention offers solutions to the problems of
preparing a multilayer structure that is suitable for use as a
synthetic leather, and that can be free from surface flaws and free
from organic solvents, yet meets the national and/or industry
requirements for adhesion strength and bally flex property, and
desirable to have sufficient abrasion resistance for use in
applications such as in automotives.
[0011] Surprisingly, an aqueous-based process produces a multilayer
structure that can be free from surface flaws. The multilayer
structure disclosed herein combines a specific skin layer with a PU
foam and fabric. Such combination surprisingly provides the
multilayer structure with an adhesion strength of 1,000 g/cm or
more as measured by Method SLF11, and passes 10,000 times of bally
flex test as measured by GB/T 8949-1995 standard. Moreover, the
multilayer structure disclosed herein comprising an additional
finishing layer can afford sufficient abrasion resistance as
evidenced by no surface cracking and no peeling off, as determined
by the test method described in ASTM D3884-01.The process disclosed
herein is also able to simultaneously prepare a multilayer
structure having an embossed surface while maintaining the above
adhesion strength and ball flex property.
[0012] In a first aspect, the present invention is a multilayer
structure comprising:
[0013] (a) a fabric,
[0014] (b) a polyurethane foam containing a plurality of cells
defined therein, wherein the foam contains at least one surfactant,
and
[0015] (c) a skin layer,
[0016] wherein the skin layer comprises a wetting agent and an
acrylic polymer having a glass transition temperature of -20 degree
Celsius (.degree. C.) or less, and the foam resides between the
fabric and the skin layer.
[0017] In a second aspect, the present invention is a process for
preparing the multilayer structure of the first aspect. The process
comprises the steps of:
[0018] (i) providing a polyurethane foam coated on a fabric,
wherein the foam contains a plurality of cells defined therein and
at least one surfactant,
[0019] (ii) providing a release paper,
[0020] (iii) providing a skin layer,
[0021] (iv) attaching the foam to the release paper with the skin
layer therebetween to form a release sheet, so that the foam
resides between the skin layer and the fabric; wherein the skin
layer comprises a wetting agent and an acrylic polymer having a
glass transition temperature of -20.degree. C. or less, and
[0022] (v) removing the release paper from the release sheet.
[0023] The process disclosed herein is useful for preparing the
multilayer structure disclosed herein. The multilayer structure
disclosed herein is useful as synthetic leather in applications
such as automotive applications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a schematic illustration of a cross-section of one
embodiment of a multilayer structure described herein.
[0025] FIG. 2 is a scan electron microscopy (SEM) image of a
cross-section of one embodiment of a multilayer structure described
herein.
[0026] FIG. 3 is a SEM image of a cross-section of a multilayer
structure embossed by a conventional direct embossing machine.
DESCRIPTION
[0027] Test methods refer to the most recent test method as of the
priority date of this document when a date is not indicated with
the test method number. References to test methods contain both a
reference to the testing society and the test method number. The
following test method abbreviations and identifiers apply herein:
ASTM refers to ASTM
[0028] International. GB refers Guo Biao.
[0029] "And/or" means "and, or as an alternative". All ranges
include endpoints unless otherwise indicated.
[0030] The use of the term "(meth)" followed by another term such
as acrylate in the present invention, refers to acrylate,
methacrylate and mixtures thereof.
[0031] "Acrylic" means (meth)acrylic acid, (meth)alkyl acrylate,
(meth)acrylamide, (meth)acrylonitrile and modified forms thereof,
such as (meth)hydroxyalkyl acrylate.
[0032] Adhesion strength of a multilayer structure refers to
interlayer adhesion strength between any two adjacent layers of the
multilayer structure.
[0033] The present invention is a multilayer structure comprising a
polyurethane (PU) foam that may comprise opposing primary surfaces.
A "primary surface" is a surface having a planar surface area equal
to the largest planar surface area of any surface of an article.
Opposing primary surfaces refers to a primary surface of an article
and a surface opposing the primary surface, the surface opposing
the primary surface generally also being a primary surface. Planar
surface area refers to the area of a surface as projected onto a
plane so as to neglect surface area contributions due to contour
features (for example, peaks and valleys) in the surface.
[0034] The PU foam in the present invention comprises a continuous
PU matrix that defines a plurality of cells therein. The PU foam in
the present invention contains one or more surfactant. The
surfactant is a characteristic of having been made from a frothed
composition comprising an aqueous PU dispersion (PUD) and is a
surfactant that can stabilize air bubbles in the aqueous PUD when
preparing the frothed composition. Another characteristic of a foam
made from an aqueous PUD is that the foam can be free from organic
solvents. The PU foam in the present invention is different from a
PU foam that is made from solvent-based compositions (as opposed to
an aqueous PUD). A PU foam made from solvent-based compositions
contains organic solvents, and is free from surfactant. Examples of
suitable surfactants in the foam include cationic, anionic, or
nonionic surfactants. Suitable surfactants include, for example,
sulfates of ethoxylated phenols such as
poly(oxy-1,2-ethanediyl).alpha.-sulfo-.omega.(nonylphenoxy)
ammonium salt; alkali metal fatty acid salts such as alkali metal
oleates and stearates; polyoxyalkylene nonionics such as
polyethylene oxide, polypropylene oxide, polybutylene oxide, and
copolymers thereof; alcohol alkoxylates; ethoxylated fatty acid
esters and alkylphenol ethoxylates; alkali metal lauryl sulfates;
amine lauryl sulfates such as triethanolamine lauryl sulfate;
quaternary ammonium surfactants; alkali metal alkylbenzene
sulfonates such as branched and linear sodium dodecylbenzene
sulfonates; amine alkyl benzene sulfonates such as triethanolamine
dodecylbenzene sulfonate; anionic and nonionic fluorocarbon
surfactants such as fluorinated alkyl esters and alkali metal
perfluoroalkyl sulfonates; organosilicon surfactants such as
modified polydimethylsiloxanes; and alkali metal soaps of modified
resins; and mixtures thereof. Preferably, the surfactant is
selected from alkali metal fatty acid salts such as alkali metal
oleates, alkali metal stearates and mixtures thereof.
Representative examples of suitable surfactants include disodium
octadecyl sulfosuccinimate, sodium dodecylbenzene sulfonate, sodium
stearate and ammonium stearate. At least one surfactant in the foam
is desirably amphoteric (for example, cocamidopropyl betaine). The
foam useful in the present invention can comprise at least two
surfactants, which are selected from ammonium stearate,
cocamidopropyl betaine and disodium octadecyl sulfosuccinimate.
Preferably, at least one surfactant is ammonium stearate.
[0035] The content of the surfactant in the foam may be from 0.05
weight percent (wt %) or more, 0.1 wt % or more, or even 0.2 wt %
or more, and at the same time, desirably 10 wt % or less, 5 wt % or
less, or even 3 wt % or less. Weight percentage of the surfactant
is based on the weight of the foam.
[0036] The foam in the present invention may comprise one or more
thickener (also known as rheology modifier). The thickener may be
non-associative or associative. It may be a cellulose ether
derivative, natural gum alkali swellable thickener, a clay material
(such as bentonite), an acid derivative, an acid copolymer, a
urethane associate thickener (UAT), a polyether urea polyurethane
(PEUPU), a polyether polyurethane (PEPU), a hydrophobically
modified ethoxylated urethane (HEUR) or mixtures thereof.
Preferably, the thickener does not cause an aqueous PUD to become
unstable. More preferably, the thickener is a water swellable
thickener that is not ionized. Examples of useful thickeners
include methyl cellulose ethers, alkali swellable thickeners (for
example, sodium or ammonium neutralized acrylic acid polymers),
hydrophobically modified alkali swellable thickeners (for example,
hydrophobically modified acrylic acid copolymers), associative
thickeners (for example, hydrophobically modified
ethylene-oxide-based urethane block copolymers), and mixtures
thereof.
[0037] Preferably, the thickener in the foam is based on an acrylic
acid copolymer, for example, ethylene acrylic acid copolymer.
Suitable commercially available thickeners include for example
ACUSOL.TM. 810 A acrylic acid copolymer available from The Dow
Chemical Company (ACUSOL is a trademark of Rohm and Haas Company).
When present, the amount of the thickener may be generally 0.1 to 5
wt %, preferably 0.2 to 3 wt %, based on the weight of the
foam.
[0038] The foam in the present invention may optionally comprise
one or more additional additives known in the art. Examples of
suitable additives include, fillers such as wood fibers, calcium
carbonate (CaCO.sub.3), silicon dioxide (SiO.sub.2), titanium
dioxide (TiO.sub.2), magnesium oxide, aluminium oxide, talc, barium
carbonate (BaCO.sub.3), barium sulfate (BaSO.sub.4), glass beads or
combinations thereof; a thickeners; flame retardants; pigments;
flowing additives; hand-feel modifiers (for example, organic
silicon compounds); antioxidants (for example, polymeric hindered
phenol resins); anti-ultraviolet additives; antistatic agents;
antimicrobial agents; and combinations thereof. Typically, these
additives may be in amount of 0 to 80 wt %, preferably 0 to 50 wt
%, and more preferably 0 to 30 wt %, based on the weight of the
foam.
[0039] The fabrics disclosed herein may comprise a flexible
polymeric material that can be, for example, woven, nonwoven,
knitted, plained or spunbond. The fabric can comprise natural
and/or synthetic fibers. Fabrics useful in the present invention
may comprise for example cotton, wool, hemp, silk, synthetic fibers
based on polyolefins (for example, polyethylene or polypropylene),
nylon, polyester, polyurethane (for example, a spandex material),
polyamides, acrylic polymers, polyvinyl chlorides, polyvinylidene
chlorides, polyvinyl alcohols, or mixtures thereof. The preferred
fabric is prepared from polyester, polyethylene or polypropylene,
or their mixtures with natural fibers. The fabric can have, or not,
characteristics resulting from a pre-treatment, such as corona
surface treatment and/or impregnation.
[0040] In the multilayer structure disclosed herein, the fabric and
a skin layer are desirably on opposing primary surfaces of the
foam. For example, it is desirable that the skin layer contacts one
primary surface of the foam and the fabric contacts an opposing
primary surface of the foam, thereby forming the multilayer
structure comprising the foam residing between the skin layer and
the fabric.
[0041] The skin layer in the present invention comprises a wetting
agent and an acrylic polymer. The acrylic polymer has a glass
transition temperature (T.sub.g) of -20.degree. C. or lower,
preferably -25.degree. C. or lower, more preferably -30.degree. C.
or lower, and most preferably -35.degree. C. or lower. At the same
time, the acrylic polymer desirably has a T.sub.g of -50.degree. C.
or higher. Measure T.sub.g by differential scanning calorimetry
(DSC) taking the inflection point in the thermogram as the T.sub.g
value.
[0042] The acrylic polymer useful in the present invention may
function as a binder in the skin layer. The acrylic polymer can be
a copolymer including at least one copolymerized ethylenically
unsaturated monomer and from 0.4 to 10 wt %, preferably from 0.4 to
4 wt %, of copolymerized acetoacetate or acetoacetamide monomer,
where wt % is relative to the total weight of monomers. Suitable
ethylenically unsaturated monomers include for example a
(meth)acrylic ester monomer including methyl acrylate, ethyl
acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate,
lauryl acrylate, methyl methacrylate, butyl methacrylate, isodecyl
methacrylate, lauryl methacrylate, hydroxyethyl methacrylate,
hydroxypropyl methacrylate, aminoalkyl (meth)acrylates; styrene or
substituted styrenes; butadiene; vinyl acetate or other vinyl
esters; vinyl monomers such as vinyl chloride, vinylidene chloride,
N-vinyl pyrollidone; and acrylonitrile or methacrylonitrile.
Preferred is the absence of copolymerized monomers containing
functional group(s) capable of chemical reaction with acetoacetate
or acetamide groups, for example, aldehyde and amine groups.
Preferably, the acrylic polymer contains 25-65 wt % copolymerized
ethyl acrylate, based on acrylic polymer weight.
[0043] The acrylic polymer useful in the present invention may be
available in the form of an aqueous emulsion. The acrylic polymer
emulsion generally has a solids content of from 25 to 40 wt %, or
even from 30 to 35 wt %. Suitable commercially available acrylic
polymer useful in the present invention may include for example
HYDRHOLAC.TM. Cl-1 emulsion (HYDRHOLAC is a trademark of ROHM and
HAAS Company) available from The Dow Chemical Company.
[0044] The content of the acrylic polymer in the skin layer is
desirably 10 wt % or more, preferably 15 wt % or more, more
preferably 20 wt % or more, and most preferably 30 wt % or more. At
the same time, the content of the acrylic polymer is desirably 95
wt % or less, preferably 85 wt % or less, more preferably 80 wt %
or less, and most preferably 75 wt % or less. Weight percentage of
the acrylic polymer is based on the weight of the skin layer. If
the content of the acrylic polymer in the skin layer is lower than
10 wt %, adhesion and bally flex properties of the resultant
multilayer structure may be compromised.
[0045] The skin layer in the present invention also comprises one
or more wetting agent (also known as leveling agent). The wetting
agent may be any compound comprising one or more surface active
compound that facilitates flow or wetting of a surface. Wetting
agents can be anion, nonionic, or cationic surfactant. Examples of
wetting agents include fluorine-containing surfactants,
silicone-containing surfactants such as polysiloxane, alkyl
poly(ethylene oxide) surfactants, and mixtures thereof. Preferably,
the wetting agent is a silicon-containing compound. More
preferably, the wetting agent is a polyalkyl siloxane surfactant.
Suitable commercially available wetting agents useful in the
present invention may include for example AQUADERM.TM. Fluid H
wetting agent available from Lanxess Company (AQUADERM is a
trademark of Lanxess Deutschland GmbH).
[0046] The content of the wetting agent in the skin layer is
desirably 0.1 wt % or more, preferably 0.3 wt % or more, more
preferably 0.4 wt % or more, and most preferably 0.5 wt % or more.
At the same time, the content of the wetting agent is desirably 1.5
wt % or less, preferably 1 wt % or less, and more preferably 0.8 wt
% or less. Weight percentage of the wetting agent is based on the
weight of the skin layer.
[0047] The skin layer, in addition to the previously described
acrylic polymer having T.sub.g of -20.degree. C., may also comprise
one or more additional polymer as an additional binder. The
additional polymers can be any film-forming polymers known in the
art, such as water-dispersible polymers. Suitable additional
polymers include for example other acrylic polymer, polyurethane,
polyurethane-acrylic hybrid or mixtures thereof. Preferably, the
skin layer comprises polyurethane as the additional binder.
Surprisingly, the combination of the polyurethane with the acrylic
polymer having T.sub.g of -20.degree. C. or less described above
can further increase adhesion strength of the resultant multilayer
structure, while still passing 10,000 times of bally flex test.
Suitable polyurethanes and other acrylic polymers for use in the
skin layer include those in commercially available PUDs such as
BAYDERM.TM. 51 UD, BAYDERM 91UD (BAYDERM is a trademark of Bayer),
and polyacrylate emulsions such as PRIMAL.TM. SC1-385, PRIMAL
SB-155 (PRIMAL is a trademark of Rohm and Haas Company), all
available from The Dow Chemical Company, and mixtures thereof.
[0048] When present in the skin layer, the additional polymer
binder is desirably present in an amount of 2 wt % or more,
preferably 5 wt % or more, and more preferably 10 wt % or more. At
the same time, the concentration of the additional polymer binder
is desirably 60 wt % or less, preferably 55 wt % or less, and more
preferably 50 wt % or less. Weight percentage of the additional
polymer binder is based on the total weight of the binders in the
skin layer. If the concentration of the additional polymer binder
is more than 60 wt %, the resultant multilayer structure may not
achieve both the previous described bally flex property and
adhesion strength.
[0049] The skin layer in the present invention may optionally
comprise one or more matting agent (also known as a duller). The
matting agent may be any microparticulate system producing a
dulling effect. The matting agent can be an inorganic matting
agent, an organic matting agent, or mixtures thereof. Examples of
suitable matting agents include silica, carbonate, kaolin,
phyllosilicates, talc, titania, zinc oxides, zirconium oxides,
alkali hydroxides, polycondensate plastics (for example, polyurea),
PU beads or polyacrylic beads dispersed in water, and mixtures
thereof. The presence of the matting agent in the skin layer may be
also helpful in enhancing coating film strength, thus increasing
abrasion resistance of the resultant multilayer structure. Suitable
commercially available matting agents useful in the present
invention may include for example HYDRHOLAC UD-2 and HYDRHOLAC UD-4
dispersions available from The Dow Chemical Company, DEUTERON.TM.
MK matting agent available from Deuteron (DEUTERON is a trademark
of Silke Wankum), and mixtures thereof. The concentration of the
matting agent in the skin layer is generally from 0 to 60 wt %,
preferably from 5 to 50 wt %, based on the total weight of the skin
layer.
[0050] The skin layer in the present invention may optionally
comprise one or more hand-feel modifier. Hand-feel modifiers may
migrate toward surfaces to adjust the hand feel of the multilayer
structure. Examples of hand-feel modifiers include organic silicon
compounds such as (organo)siloxanes and their copolymers, oils,
waxes, and mixtures thereof. When the skin layer further comprises
a silicon-containing hand-feel modifier, the surface of the
resultant multilayer structure can have increased water repellency
property. The hand-feel modifiers can be available in the form of
an aqueous dispersion having a solids content of up to 60 wt %.
Suitable commercially available hand-feel modifiers useful in the
present invention may include for example ROSILK.TM. 2229 feel
modifier available from The Dow Chemical Company (ROSILK is a
trademark of Rohm and Haas Company).
[0051] When present, the content of hand-feel modifiers is
generally up to 10 wt %, preferably up to 8 wt %, and more
preferably up to 3 wt %, and at the same time, the amount of the
hand-feel modifiers is desirably 0.1 wt % or more, and preferably
0.5 wt % or more. Weight percentage of the hand-feel modifier is
based on the total weight of the skin layer. If the content of the
hand-feel modifier is more than 10 wt %, the skin layer may be
slippery or waxy.
[0052] The skin layer in the present invention may optionally
comprise pigments and/or colorants. Pigments and/or colorants may
be added so as to prepare a transparent or translucent film with a
desired color. Examples of pigments or colorants may include iron
oxides, opacifying pigments (for example, titanium oxide, carbon
black), opacifying polymers and mixtures thereof. Pigments and/or
colorants may be added in an amount of 0 to 120 parts per hundred
parts of total binders in the skin layer. Suitable commercially
available black pigments useful in the present invention may
include for example EUDERM.TM. black BN carbon black dispersion
available from Lanxess Company (EUDERM is a trademark of Lanxess
Deutschland GmbH).
[0053] The skin layer in the present invention may optionally
comprise one or more thickener. Suitable thickeners include those
described in the foam. The thickeners in the skin layer are
desirably selected from alkali swellable emulsions (ASE),
hydrophobically-modified alkaline swellable emulsions (HASE),
hydrophobically modified ethyleneoxide-urethane polymers (HEUR),
hydrophobically-modified cellulosics, hydrophobically-modified
polyacrylamides, inorganic clay materials (such as bentonite),
hydroxyethyl cellulose (HEC), and mixtures thereof. Suitable
commercially available thickeners useful in the present invention
may include for example PRIMAL RM-1020 and PRIMAL RM-825 thickeners
available from The Dow Chemical Company. The amount of the
thickener in the skin layer is generally up to 20 wt %, preferably
up to 10 wt %, based on the weight of the skin layer.
[0054] The skin layer in the present invention can further
comprise, or be free from, any one or combination of more than one
of the following additives: plasticizers such as dioctyladipate or
dioctylphthalate in an amount of up to 20 wt %, preferably up to 2
wt %; antifoaming agents, antioxidants, or ultraviolet (UV) light
absorbing agents in an amount of up to 5 wt %, preferably up to 1.0
wt %; and flame retardants in an amount of up to 5 wt %. Weight
percentage of the additives is based on the weight of the skin
layer.
[0055] The multilayer structure disclosed herein may further
comprise a finishing layer, so that the skin layer is between the
finishing layer and the foam. The presence of the finishing layer
can further increase abrasion resistance of the multilayer
structure comprising thereof. The finishing layer may comprise a
wetting agent, and a crosslinked acrylic polymer wherein the
acrylic polymer has a T.sub.g of -20.degree. C. or lower. The
acrylic polymer is as described in the skin layer. The content of
the crosslinked acrylic polymer in the finishing layer is desirably
10 wt % or more, preferably 15 wt % or more, more preferably 20 wt
% or more, and most preferably 25 wt % or more. At the same time,
the content of the acrylic polymer is desirably 95 wt % or less,
preferably 85 wt % or less, more preferably 50 wt % or less, and
most preferably 35 wt % or less. Weight percentage of the
crosslinked acrylic polymer is based on the weight of the finishing
layer. The wetting agent and its concentration in the finishing
layer are as described in the skin layer, with wt % relative to the
finishing layer weight.
[0056] When present in the multilayer structure, the finishing
layer can also comprise one or more than one polymer suitable for
use in the skin layer. Desirably, the finishing layer comprises
non-crosslinked acrylic polymer having a T.sub.g of -20.degree. C.
or lower to achieve desirably bally flex property. When the skin
layer contains polyurethane as the additional binder, the finishing
layer also desirably comprises polyurethane so as to further
improve adhesion strength of the resultant multilayer structure.
More preferably, the finishing layer comprises crosslinked
polyurethane. The polyurethane is as described in the skin layer.
The finishing layer may also optionally comprise other components
(for example, matting agent, hand-feel modifier, pigments and/or
colorants, thickener or optional additives) as described in the
skin layer. In addition to the skin layer or both the skin layer
and the finishing layer, the multilayer structure disclosed herein
can further comprise one or more than one optional additional layer
such as a color layer between the skin layer and the finishing
layer. Other suitable optional additional layers can be selected
from a water repellent layer, UV protective layer and tactile
(touch/feel) modification layer. Each of these other suitable
optional additional layers, if present, is located with the skin
layer between it and the foam.
[0057] The multilayer structure disclosed herein may further
comprise a release paper, wherein the skin layer resides between
the foam and the release paper. When the multilayer structure also
comprises the finishing layer described above, the finishing layer
resides between the skin layer and release paper, and the skin
layer resides between the finishing layer and the foam.
[0058] The multilayer structure disclosed herein does not require
an adhesive to attach the PU foam to the fabric. That is, the
multilayer structure can be free of an adhesive between the PU foam
and the fabric. Preferably, the multilayer structure has no
detectable organic solvent, that is, the multilayer structure is
free of organic solvents.
[0059] The multilayer structure disclosed herein desirably has no
surface flaw, that is, free from surface flaws. "No surface flaws"
and "free from surface flaws" means that the surface has no holes
or cracks by visual observation. If the multilayer structure has an
embossed surface, the embossing patterns can be evenly distributed
on the surface.
[0060] The multilayer structure disclosed herein desirably has an
adhesion strength of 1,000 g/cm or more according to Method SLF11,
preferably 1,200 g/cm or more, and more preferably 1,500 g/cm or
more. In addition, the multilayer structure disclosed herein is
able to pass 10,000 times of bally flex test according to GB/T
8949-1995 standard.
[0061] The multilayer structure disclosed herein, in particular
comprising the finishing layer, may afford sufficient abrasion
resistance, that is no surface cracking and no peeling off, as
determined by the test method described in ASTM D3884-01.
[0062] The multilayer structure disclosed herein may have a gloss
of 80 degrees)(.degree. or less, 60.degree. or less, 10.degree. or
less, or even 2.degree. or less, as measured according to ASTM
D5767 1999.
[0063] The multilayer structure disclosed herein can include a
design in the form of an image and/or textured pattern on one or
more than one exposed surface. Such a design can be imparted onto a
surface of the multilayer structure during or after formation of
the multilayer structure. For example embossing or imprinting with
an image (using ink or dye for example) can occur by any method
known in the art including compression embossing by pressing with a
heated patterned platen, rolling or spraying ink or dye onto a
surface or imprinting with a texture via a textured release
sheet.
[0064] The multilayer structure disclosed herein can be cut or
otherwise shaped so as to have a shape suitable for any desired
purpose, such as shoe manufacturing. The multilayer structure
disclosed herein may be used in various applications particularly
suitable for use as synthetic leather, for example, footwear,
handbags, belts, purses, garments, furniture upholstery, automotive
upholstery, and gloves. The multilayer structure is particular
suitable for use in automotive applications.
[0065] The process disclosed herein is suitable for preparing the
multilayer structure disclosed herein. The process disclosed herein
comprise the following steps: (i) providing a polyurethane foam
coated on a fabric, wherein the foam contains a plurality of cells
defined therein and at least one surfactant, (ii) providing a
release paper, (iii) providing a skin layer, (iv) attaching the
foam to the release paper with the skin layer therebetween to form
a release sheet, so that the foam resides between the skin layer
and the fabric; wherein the skin layer comprises a wetting agent
and an acrylic polymer having a glass transition temperature of
-20.degree. C. or less, and (v) removing the release paper from the
release sheet. In step (i) of the process disclosed herein, the
foam can be made from a frothed composition comprising an aqueous
PUD, one or more surfactant that can stabilize air bubbles in the
aqueous PUD when preparing the frothed composition described above,
and optionally one or more thickener and additional additive
described with respect to the foam above. The surfactant(s), and
the thickener and additive (if present) may be added to the PUD or
the PUD may be added to the surfactant(s).The frothed composition
may comprise 50 to 99 wt % of aqueous PUD, preferably 60 to 99 wt
%, based on the total weight of the frothed composition.
[0066] The aqueous PUD in the frothed composition can be an
externally stabilized polyurethane dispersion or an internally
stabilized polyurethane dispersion.
[0067] "Internally stabilized polyurethane dispersion" herein
refers to a polyurethane dispersion that is stabilized through the
incorporation of ionically or nonionically hydrophilic pendant
groups within the polyurethane particles dispersed in the liquid
medium. Examples of nonionic internally stabilized polyurethane
dispersions are described in U.S. Pat. Nos. 3,905,929 and
3,920,598. Ionic internally stabilized polyurethane dispersions are
well known and are described in U.S. Pat. No. 6,231,926. Typically,
dihydroxyalkylcarboxylic acids such as described in U.S. Pat. No.
3,412,054 are used to make anionic internally stabilized
polyurethane dispersions. A common monomer used to make an anionic
internally stabilized polyurethane dispersion is
dimethylolpropionic acid (DMPA).
[0068] Preferably, the aqueous PUD in the frothed composition is an
externally stabilized polyurethane dispersion. "Externally
stabilized polyurethane dispersion" herein refers to a polyurethane
dispersion that substantially fails to have an ionic or nonionic
hydrophilic pendant groups and thus requires the addition of a
surfactant to stabilize the polyurethane dispersion. The surfactant
can be those described in the foam above. Examples of externally
stabilized polyurethane dispersions are described in U.S. Pat. Nos.
2,968,575; 5,539,021; 5,688,842 and 5,959,027.
[0069] Methods of preparing the foam by the frothed composition are
known to those skilled in the art including, for example, a process
described in W02005/061198A1. One method of preparing the foam may
comprise the steps of: (I) frothing a composition comprising the
aqueous PUD, the surfactant, and optionally the thickener and
additional additive described above to prepare the frothed
composition, (II) applying the frothed composition to the fabric
described above to form a coated fabric; (III) drying the coated
fabric, that is, exposing the coated fabric to drying conditions
for drying the frothed composition, and optionally passing through
a pressing roller. Thus, a fabric coated with the PU foam forms.
The method of preparing the foam generally also includes adjusting
the thickness of the frothed composition on the fabric, after step
(II) applying the frothed composition to the fabric described above
to form a coated fabric.
[0070] The release paper useful in the process may be any release
paper known in the art. The release paper generally has a
hydrophobic surface. The release paper suitable for the present
invention may have a flat surface or an embossed surface with
patterns. Preferably, an embossed release paper, that is, a
textured release paper, is used. The release paper may have various
embossed patterns known in the art, such as texture of natural
leather grain.
[0071] In step (iii) of the process disclosed herein, the skin
layer can be prepared from an aqueous skin coating composition. The
aqueous skin coating composition may comprise the wetting agent,
the acrylic polymer having T.sub.g of -20.degree. C. or less as the
binder, and other optional components (for example, additional
polymers as the additional binder, matting agent, hand-feel
modifiers, pigments and/or colorants, thickener, additives)
described above in the skin layer. The acrylic polymer can be in
the form of an aqueous dispersion or emulsion, and mixed with other
ingredients in any order to form the skin coating composition.
Preferably, the aqueous skin coating composition comprises an
aqueous polyurethane dispersion. When present, the polyurethane
dispersion desirably has a film modulus of 2.5 megapascals (MPa) or
less, 2.3 MPa or less, or even 2 MPa or less, so as to maintain the
flexibility of the resultant skin layer. The solids weight of the
aqueous skin coating composition is the same as the total weight of
the skin layer. The concentration of each component in the aqueous
skin coating composition can be obtained from the previously
described concentration of the component in the skin layer. As an
example, the acrylic polymer in the aqueous skin coating
composition can be in an amount of from 10 weight percent to 95
weight percent, where weight percentage is based on the solids
weight of the skin coating composition. In addition, water or
diluents may be added as necessary into the aqueous skin coating
composition to control the solids of the skin coating composition
to a desired range. The aqueous skin coating composition useful in
the present invention generally has a solids content of 20 wt % or
more, 30 wt % or more, or even 40 wt % or more, and at the same
time, generally 80 wt % or less, 70 wt % or less, or even 60 wt %
or less, based on the total weight of the aqueous skin coating
composition.
[0072] Viscosity of the aqueous skin coating composition is
generally 500 centipoise (cps) or higher, 1,000 cps or higher, and
at the same time, is generally 20,000 cps or lower, 15,000 cps or
lower at 25.degree. C. measured in accordance with ASTM D5125. If
the viscosity is lower than 500 cps, the thickness of the dried
coating film formed therefrom may be inconsistent. If the viscosity
is higher than 20,000 cps, the skin coating composition may be
difficult to level into the entire surface of a substrate to be
coated.
[0073] To form the skin layer, the aqueous skin coating composition
can be applied to, and adhered to a substrate (for example, the
foam, other layer(s) of the multilayer structure disclosed herein,
or preferably, the release paper) by conventional means such as
brushing, dipping spraying and rolling coating, then dried and
cured. The standard spray techniques and equipment for air spraying
and electrostatic spraying, such as electrostatic bell application
and either manual or automatic methods can be used. Preferably,
rolling coating is used.
[0074] In the process disclosed herein, the release sheet can be
obtained by the following steps: applying an aqueous skin coating
composition to the foam, the release paper, or both the foam and
the release paper, attaching the foam to the release paper with the
aqueous skin coating composition therebetween, drying the aqueous
skin coating composition to form the skin layer, and applying
pressure to the resultant sheet, that is, pressing the resultant
sheet. The above steps in preparing the release sheet can be
conducted in a different order. For example, the process disclosed
herein preferably includes firstly applying the aqueous skin
coating composition to a textured release paper, followed by drying
or at least partially drying the skin coating composition. Thus,
the textured patterns on the release paper can be easily
transferred to the skin layer of the resultant multilayer structure
resulting in an embossed pattern on the skin layer. Drying the skin
coating composition is preferably conducted before attaching to the
foam, so that it can afford fast production speed without causing
surface flaws on the resultant multilayer structure. When the
aqueous skin coating composition is coated onto the foam, the
coated foam is preferably partially dried before contacting the
foam to the release paper, so as to balance quality of the patterns
on the surface of the resultant multilayer structure and the
production speed. Alternatively, pressure may be applied before
drying the skin coating composition, which may be helpful to ensure
close contact between different layers of the resultant multilayer
structure. Applying pressure can be conducted prior to, during,
and/or after drying the aqueous skin coating composition.
[0075] Preferably, the release sheet useful in the present
invention is prepared by applying the aqueous skin coating
composition to the release paper, drying the aqueous skin coating
composition to form the skin layer, contacting the foam to the
release paper with the skin layer therebetween, and applying
pressure to the resultant sheet. One or more additional step of
applying pressure may be used before drying the skin coating
composition.
[0076] In step (v) of the process disclosed herein, the release
paper is removed from the release sheet. Removing the release paper
can be done by peeling the release paper from the release sheet.
There is no residual left on the surface of the release paper after
being peeling off from the release sheet, so the release paper can
be recycled for re-use. The process disclosed herein may further
comprise one or more pressing step after removing the release paper
from the release sheet.
[0077] The process disclosed herein may further comprise the steps
of: applying an aqueous finishing composition to the release paper
in step (ii), then drying the aqueous finishing composition to form
a finishing layer coated on the release paper; so that the skin
layer resides between the foam and the finishing layer.
Alternatively, the process disclosed herein may include applying
the aqueous finishing composition to the skin layer of the
multilayer structure obtained after step (v); then drying the
aqueous finishing composition to form a finishing layer; so that
the multilayer structure comprises the skin layer residing between
the foam and the finishing layer. The aqueous finishing composition
is the same as described above. The viscosity of the finishing
composition may be the same as that of the skin coating
composition.
[0078] The finishing layer in the process disclosed herein is made
from the aqueous finishing composition. The aqueous finishing
composition may comprise the wetting agent described above, an
acrylic polymer emulsion, wherein the acrylic polymer has a glass
transition temperature of -20.degree. C. or lower as describe
above, a crosslinking agent and optional components (for example,
additional polymer binder, matting agent, hand-feel modifier,
pigments and/or colorants, thickener and optional additives)
described above. The acrylic polymer can be in the form of an
aqueous dispersion or emulsion, and mixed with other ingredients in
any order to form the finishing composition. Except for the
crosslinking agent in the finishing composition, the concentration
ranges of all other ingredients in the finishing composition can be
the same as the aqueous skin coating composition for preparing the
skin layer. Preferably, the aqueous finishing composition comprises
an aqueous polyurethane dispersion. When present, the polyurethane
dispersion in the finishing composition desirably has a film
modulus of 2.5 MPa or higher, 2.7 MPa or higher, or even 3 MPa or
higher, so as to further increase the abrasion resistance of the
resultant multilayer structure.
[0079] The crosslinking agent in the aqueous finishing composition
can be any compound that can crosslink the acrylic polymer. The
crosslinking agent desirably can also crosslink polyurethane. The
crosslinking agent may comprise amine crosslinking agents,
amide-aldehyde condensates, polyisocyanate crosslinking agents or
mixtures thereof. Suitable crosslinking agents may include for
example those crosslinking agents described in U.S. Pat. No.
5,071,904. Representative examples of the crosslinking agent
include polyisocyanates, polyazirdines, aminoplast resins and
mixtures thereof. Preferably, polyisocyanate crosslinking agents
are used. Suitable commercially available crosslinking agents
useful in the present invention may include for example BAYDERM
XL-50, BAYDERM XL-60 and BAYDERM XL-90 polyisocyanates all
available from Lanxess Company, and mixtures thereof. The
crosslinking agent is desirably in an amount that can partially
crosslink the acrylic polymer in the finishing composition. The
concentration of the crosslinking agent in the finishing
composition may be 0.1 wt % or more, preferably 0.2 wt % or more,
and more preferably 0.5 wt % or more. At the same time, the
concentration of the crosslinking agent is desirably 50 wt % or
less, preferably 40 wt % or less, and more preferably 35 wt % or
less. Weight percentage of the crosslinking agent is based on the
total weight of the aqueous finishing composition.
[0080] To form the finishing layer, the aqueous finishing
composition can be coated to a substrate by conventional means
described above.
[0081] Preferably, the process disclosed herein comprises the steps
of: applying the aqueous finishing composition to a release paper
to obtain a coated release paper, then passing the coated release
paper through an oven to dry the aqueous skin coating composition,
so as to form the finishing layer; applying the aqueous skin
coating composition to the dried finishing layer, then contacting
with the foam so that the aqueous skin coating composition resides
between the finishing layer and the foam; passing the resultant
release sheet through a pressing roller; then passing through an
oven to dry the aqueous skin coating composition; passing through a
pressing roller again; and finally removing the release paper from
the release sheet.
[0082] In the process disclosed herein, drying the aqueous skin
coating composition or, if present the aqueous finishing
composition can form the skin layer or, if present the finishing
layer. "Drying" in the present invention means a process involving,
but not limited to, the removal of water and solvent (if present)
by evaporation. Drying in the present invention can also involve
chemical reactions such as a crosslinking reaction (that is, a
curing reaction). For example, drying the aqueous finishing
composition which comprises a crosslinking agent also means drying
and curing the aqueous finishing composition. Drying may be
conducted at any temperature, so long as fully dried coating films
are formed and no component in the multilayer structure decomposes.
In particular, when drying is conducted after attaching the foam to
the release paper with aqueous compositions therebetween, water
vapor generating from these wet aqueous compositions may reside
between the release paper and the foam. Release paper is generally
impermeable to water vapor, thus water vapor tends to diffuse
through the foam and even fabric during the drying process.
Accumulated water vapor between layers may cause delamination of
the resultant multilayer structure. To avoid potential delamination
of the multilayer structure, these aqueous compositions is
desirably slowly dried; or the aqueous skin coating composition or,
if present the aqueous finishing composition is desirably firstly
applied to the release paper, and dried and cured the above aqueous
compositions before contacting with the foam.
[0083] In the process disclosed herein, time for drying the skin
coating composition and the finishing composition (if present) is
desirably 0.5 minutes or more, preferably 1 minutes or more, and
more preferably 2 minutes or more, and at the same time, is
desirably 30 minutes or less, preferably 25 minutes or less, and
more preferably 20 minutes or less. Drying step(s) is desirably
conducted at a temperature of about 90.degree. C. or more,
preferably 100.degree. C. or more, more preferably 105.degree. C.
or more, and at the same time, is desirably 200.degree. C. or less,
preferably 180.degree. C. or less, and more preferably 150.degree.
C. or less. If the drying time is less than 0.5 minutes, coating
films made therefrom may not be fully dried. If the temperature is
lower than 90.degree. C., it may take too long to fully dry the
aqueous compositions. If the temperature is higher than 150.degree.
C., too fast water evaporation during the drying step(s) may cause
flaws on the surface of the resultant multilayer structure.
[0084] In the process disclosed herein, one or more step of
applying pressure is useful to ensure all layers of the multilayer
structure to closely contact and/or adhere with each other.
Applying pressure may be conducted at conventional equipments such
a pressing roller. Applying pressure can be conducted under
conditions that have no adverse effects on the foam structure of
the PU foam in the multilayer structure. Preferably, thickness
change of a sample before and after applying pressure is up to 5%.
Depending on temperature and time used when applying pressure, the
pressure used is desirably 0.2 MPa or less, 0.15 MPa or less, or
even 0.1 MPa or less. The step of applying pressure may be
conducted at a temperature higher than T.sub.g of the acrylic
polymer binder. Preferably, applying pressure step is conducted
right after drying a sample, so that the pressing roller used for
applying pressure does not require to be heated. The step(s) of
applying pressure in the process disclosed herein is desirably
conducted at a temperature of 100.degree. C. or lower, and at the
same time, desirably 60.degree. C. or higher, 70.degree. C. or
higher, or even 90.degree. C. or higher. Time for applying pressure
may be from 10 seconds or longer, or even 20 seconds or longer, and
at the same time, 300 seconds or shorter, 200 seconds or shorter,
or even 60 seconds or shorter.
[0085] The process disclosed herein does not require the use of any
organic solvent. Preferably, no organic solvent is used in the
process, and aqueous compositions used in the process have no
detectable organic solvent present, that is, the process is free of
organic solvents.
[0086] The multilayer structure obtained from the process disclosed
herein desirably has a surface free from flaws. The multilayer
structure may have a flat surface if a release paper with a flat
surface is used, or has an embossed surface when using an embossed
release paper.
[0087] When an embossed release paper is used, the process
disclosed herein can simultaneously prepare a multilayer structure
with a surface that has a profile corresponding to that of the
release paper. Thus, the process disclosed herein does not require
the use of additional conventional embossing equipment and steps to
offer the multilayer structure with an embossed surface. If an
embossed release paper is used, the process disclosed herein is
able to prepare a multilayer structure that simultaneously has an
embossed surface that can be free from any flaws. At the same time,
the embossed multilayer structure obtained from the process
disclosed herein still has an adhesion strength of 1,000 g/cm or
more, and passes 10,000 times of bally flex test. In contrast, when
the multilayer structure disclosed herein is further embossed by a
conventional direct embossing process (that is, an embossing
process using a conventional embossing roller), the bally flex
property of the multilayer structure is significantly compromised,
which fails to pass 10,000 times of bally flex test, as described
in Comparative Example F.
[0088] Generally, the thickness of the skin layer may be 5 to 500
microns, 10 to 400 microns, 15 to 300 microns, or even 100 to 300
microns. The thickness of the foam may be 500 to 2,000 microns, 600
to 1,500 microns, or even 650 to 1,200 microns. The thickness of
the fabric may be 0.2 to 2 millimeter (mm), 0.5 to 1.5 mm, or even
0.1 to 2 mm. The thickness of the multilayer structure may be 0.8
to 3 mm, 0.9 to 2.5 mm, or even 1.0 to 1.5 mm. When present, the
finishing layer may have a thickness in the range of from 5 to 500
microns, from 10 to 400 microns, from 15 to 300 microns, or even
from 30 to 100 microns.
[0089] With reference to FIG. 1, there is shown a schematic
perspective view of one embodiment of a multilayer structure 10
disclosed herein comprising skin layer 11, foam 12, fabric 13 and
optionally one or more other layers therebetween. Each layer
comprises two opposing primary surfaces. Skin layer 11 contacts one
primary surface of foam 12 and fabric 13 contacts the opposing
primary surface of foam 12, so that foam 12 resides between skin
layer 11 and fabric 13. An optional finishing layer (not shown) may
reside on one primary surface of skin layer 11, so that skin layer
11 resides between the finishing layer and foam 12.
[0090] With reference to FIG. 2, there is shown a SEM image of a
cross-section of a multilayer structure disclosed herein. The
multilayer structure comprises foam 22.
[0091] With reference to FIG. 3, there is shown a SEM image of a
cross-section of a multilayer structure embossed by a conventional
direct embossing machine. The multilayer structure comprises foam
32.
EXAMPLES
[0092] The following examples illustrate embodiments disclosed
herein. All parts and percentages in the examples are by weight
unless otherwise indicated. The following materials are used in the
examples:
[0093] EUDERM black BN dispersion is a carbon black dispersion
having a solids content of 20 wt %, available from Lanxess
Company.
[0094] HYDRHOLAC UD-2 dispersion is an aqueous dispersion of a
fully reacted aliphatic polyurethane polymer. It contains silica
and has a solids content of 25 wt %, available from The Dow
Chemical Company.
[0095] ROSILK 2229 feel modifier is an aqueous emulsion of
polyalkyl siloxane having a solids content of 30 wt %, available
from The Dow Chemical Company.
[0096] HYDRHOLAC Cl-1 emulsion is an acrylic polymer emulsion
(T.sub.g=-40.degree. C.) having a solids content of 36-38 wt %,
available from The Dow Chemical Company.
[0097] BAYDERM 91UD dispersion is an aqueous polyurethane
dispersion (T.sub.g=-44.degree. C.), based on isophorone
diisocyanate (IPDI) and polyester polyol, stabilized by carboxylate
group(s) existing in the polyurethane backbone. It has a solids
content of 30 wt %, available from The Dow Chemical Company.
[0098] AQUADERM Fluid H wetting agent is a silicone-based wetting
agent available from Lanxess Company.
[0099] BAYDERM XL-50 crosslinking agent has around 6 wt % of active
isocyanate groups (--NCO) and is emulsifiable when mixing with
water, available from Lanxess Company.
[0100] Nappa Soft S-C is a wax and polyacrylate hybrid emulsion
used as a matting agent, available from Lanxess Company.
[0101] Matting Agent SNC is a silica-containing polyacrylate
emulsion as matting agent, available from Lanxess Company.
[0102] BAYDERM 51-UD dispersion is an aqueous polyurethane
dispersion (Tg=-54.degree. C.), based on IPDI and polyester polyol,
stabilized by carboxylate group(s) existing in the polyurethane
backbone. It has a solids content of around 30 wt %, available from
The Dow Chemical Company.
[0103] PRIMAL SC1-385 emulsion is a polyacrylate emulsion
(Tg=-12.degree. C.) having a solids content of 46-48 wt %,
available from The Dow Chemical Company.
[0104] PRIMAL SB-155 emulsion is a polyacrylate emulsion
(T.sub.g=-10.degree. C.) having a solids content of 34-36 wt %,
available from The Dow Chemical Company.
[0105] Fabric is needled cotton and polyester fiber hybrid woven
fabric, available from Fujian Nanfang Textile Co. Ltd.
[0106] An embossed release paper with patterned surface is
available from Arjowiggins.
[0107] SYNTEGRA.TM. YS3000 dispersion (SYNTEGRA is a trademark of
The Dow Chemical Company) is a polyurethane dispersion, which is a
waterborne, methylene diphenyl diisocyanate (MDI) based
polyurethane produced without the use of organic solvents. It is a
white liquid that typically has a solids content of 53-56 wt % and
a density of 1.05 grams per cubic centimeter (g/cc) at 25.degree.
C., available from The Dow Chemical Company.
[0108] Stanfax 320 ammonium stearate surfactant, Stanfax 318
disodium octadecyl sulfosuccinimate surfactant, and Stanfax 590
cocamidopropyl betaine surfactant are all available from
Para-Chem.
[0109] ACUSOL 810 acrylic acid copolymer thickener is available
from The Chemical Company.
[0110] The following standard analytical equipment and methods are
used in the Examples.
Adhesion Test
[0111] Adhesion strength of each multilayer structure was measured
in accordance with Method SLF11 adopted by Society of Leather
Technologists and Chemists. Adhesion strength refers to interlayer
adhesion strength between any two adjacent layers of the multilayer
structure. Samples with a width of one centimeter were used for
testing. The skin layer, or finishing layer (if present) of the
sample was firstly adhered to a polyvinyl chloride (PVC) test strip
using an adhesive. Increasing static loads were applied to the
multilayer structure until the sample delaminated. The maximum load
before the delamination of the sample was recorded as gram per
centimeter of sample width (g/cm).
Bally Flex Test
[0112] The bally flex property of a multilayer structure was
measured by in accordance with GB/T 8949-1995 standard. A sample
(3.8 cm by 6.5 cm) was positioned on a bally flexometer (Gotech
Company) and flexed for up to 100,000 times at ambient temperature
(from 22.degree. C. to 25.degree. C.). After flexing, the sample
was observed under an optical microscope at a 10.times. (ten times)
magnification. If no cracking and generation of "white crazing" in
the flexing area is observed, the sample passes 10,000 times of
bally flex test.
Abrasion Test
[0113] The abrasion resistance of a multilayer structure was
measured in accordance with ASTM D3884-01 test (H-18 wheel, 1.0
kilogram (Kg), 500 cycles). If no cracking or peeling off was
observed on the surface of a sample, the sample passed the abrasion
test. In addition, lower weight loss of a sample after the abrasion
test means better abrasion resistance.
Evaluation of Surface Flaw
[0114] The surface of the skin layer, or the finishing layer (if
present) of a multilayer structure was visually observed. If no
flaw (that is, no cracks or holes) was observed on the surface of
the multilayer structure, it indicates the multilayer structure has
no surface flaw.
Preparation of a PU Foam
[0115] The PU foam was made using a frothed composition containing
PUD. 1200 grams (g) of SYNTEGRA 3000 PU dispersion having a solids
content of 53-56 percent by weight, 48.0 g of ammonium stearate
(Stanfax 320), 15.6 g of disodium octadecyl sulfosuccinimate
(Stanfax 318), 13.5 g of cocamidopropyl betaine (Stanfax 590) and
79.4 g of ACUSOL 810A acrylic acid copolymer thickener were mixed.
The viscosity of the thickened PUD was around 23,300 cP measured
using a Brookfiled viscometer with a #6 spindle at 20 revolutions
per minute (rpm). A fabric was attached to pin frame. The mixture
was frothed using a Model 2MT1A foam machine (E.T. OAKES Corp.) run
at 1000 rpm. The density of the resultant wet froth is about 0.69
g/cm.sup.3. The froth was applied to fixed fabric using a Labcoater
type LTE-S(Werner Mathis AG). The doctor knife was positioned at
1.8-2.5 mm between the roller and knife (including resin and
fabric). The resultant frothed dispersion was coated on the fabric
by the doctor knife. The coated fabric was then placed in an oven
at 100.degree. C. for 6 to 10 minutes, and then heated to
170.degree. C. in about 5 minutes to form the PU foam coated on the
fabric.
Preparation of Aqueous Coating Compositions
[0116] Aqueous coating compositions (Coatings 1-4, Comparative
Coatings A-F) were prepared as follows. The ingredients in these
coating compositions are described in Table 1. Firstly, pigment(s)
was dispersed in water by a high shear mixer (COWLES mixer) to form
a pre-dispersed pigment paste. Then, binders and other components
except for thickener and crosslinking agent (if present), were
added to the pre-dispersed pigment paste under low shear stirring.
The resultant mixture was then filtered to remove agglomerated
particles. Finally, thickener and crosslinking agent (if present)
were added in to the mixture.
Examples 1-2, Comparative Examples (Comp. Ex.) A-D
[0117] Coatings 1-2 and Comparative Coatings A-D were coated on an
embossed release paper by roll knives with the knife gap of
approximately 200 microns, and then dried in an oven at 130.degree.
C. for 1 minute to form a skin layer. The resultant coated release
paper was attached to the PU foam obtained above with the skin
layer therebetween, then passed through a pressing machine (Carvel
model 4128 from Carvel Inc.) under the condition of 0.10 MPa, and
100.degree. C. for 50 seconds. The resultant release sheet was
cooled down to ambient temperature, then the release paper was
peeled off. Multilayer structures comprising the foam, the fabric
and the skin layer residing therebetween were obtained.
Example 3-5, Comp Example E
[0118] An aqueous finishing composition for preparing a finishing
layer was firstly coated on an embossed release paper by a roll
knife with the knife gap of around 60 microns, then dried in an
oven at 130.degree. C. for 0.5 minute to form the finishing layer.
The resultant finishing layer was further coated with an aqueous
skin coating composition for preparing skin layer by a roll knife
with the knife gap of around 200 microns, then dried in an oven at
130.degree. C. for 1 minute to form the skin layer. The resultant
coated release paper was attached to the PU foam obtained above
with the skin layer and finishing layer therebetween, then passed
through a pressing machine (Carvel model 4128 from Carvel Inc.)
under the condition of 0.10 MPa, and 100.degree. C. for 50 seconds.
The resultant release sheet was cooled down to ambient temperature,
then the release paper was peeled off to obtain the multilayer
structures of Example 3-5 and Comparative Example E.
TABLE-US-00001 TABLE 1 Comp. Comp. Comp. Comp. Comp. Coating 1
Coating 2 Coating 3 Coating 4 Coating A Coating B Coating C Coating
D Coating E Component Function (Values below are in grams) EUDERM
black BN Pigment 100 150 4 4 100 100 100 100 4 Nappa Soft S-C
Matting agent 100 100 -- -- 100 100 100 100 -- Matting Agent SNC
Matting agent 50 50 -- -- 50 50 50 50 -- BAYDERM 91UD Binder -- --
8 18 -- -- -- -- 38 BAYDERM 51-UD Binder -- 100 -- -- -- -- 500 500
-- HYDRHOLAC C1-1 Binder 500 480 30 20 -- -- -- -- -- PRIMAL
SC1-385 Binder -- -- -- -- 500 -- -- -- -- PRIMAL SB-155 Binder --
-- -- -- -- 500 -- -- -- AQUADERM Fluid H Wetting agent 8 8 4 4 8 8
8 -- -- HYDRHOLAC UD-2 Matting agent -- -- 80 80 -- -- -- -- 80
ROSILK 2229 Hand-feel -- -- 8 8 -- -- -- -- 8 modifier BAYDERM
XL-50 Crosslinking -- -- 21 31.5 -- -- -- -- 21 agent
[0119] Properties of the above multilayer structures were evaluated
according to the testing methods described above. Results were
given in Tables 2 and 3.
[0120] The multilayer structures of Examples 1-5 and Comparative
Examples A-C had good pattern fullness and definition. In contrast,
the multilayer structures of Comparative Examples D-E, where the
skin layer or, if present the finishing layer does not contain a
wetting agent, showed a flawed surface with holes, which does not
have a corresponding profile with the release paper.
[0121] As shown in Tables 2 and 3, the multilayer structures of
Examples 1-5 showed an adhesion strength of higher than 1,000 g/cm
and passed 100,000 times of bally flex test. The multilayer
structures of Examples 2, 4 and 5 showed even better adhesion
strength than that of Examples 1 and 3.
[0122] Abrasion resistance of the multilayer structures of Examples
3-5 was measured according to ASTM D3884-01. Each of these
multilayer structures had no surface cracking or peeling off during
the test. Weight losses for the multilayer structures of Examples
3, 4 and 5 are only 20-29 milligrams (mg), 9-18 mg, and 20-28 mg,
respectively.
[0123] In contrast, the multilayer structures of Comparative
Examples A and B had adhesion strength values less than 1,000 g/cm.
In addition, cracks were formed on the skin layer of the multilayer
structures of Comparative examples A and B after only 80,000 times
and 20,000 times of bally flex test, respectively. Although the
multilayer structure of Comparative Example C had an adhesion
strength of 3,200 g/cm, it failed 10,000 times of bally flex
test.
TABLE-US-00002 TABLE 2 Example 1 Example 2 Comp. Ex. A Comp. Ex. B
Comp. Ex. C Comp. Ex. D Skin Coating 1 Coating 2 Comp. Comp. Comp.
Comp. Coating Coating A Coating B Coating C Coating D Adhesion 1.4
2.0 0.6 0.1 3.2 -- Strength, g/cm Bally flex, 100,000 100,000
80,000 20,000 20,000 -- times Surface no surface no surface no
surface no surface no surface having flaw flaw flaw flaw flaw
flaws
TABLE-US-00003 TABLE 3 Example 3 Example 4 Example 5 Comp. Ex. E
Skin Coating Coating 1 Coating 2 Coating 2 Comp. Coating D
Finishing Coating 3 Coating 4 Coating 3 Comp. Coating Coating E
Adhesion 1,500 2,200 2,300 -- Strength, g/cm Bally Flex, 100,000
100,000 100,000 -- times Abrasion test Pass Pass Pass -- Surface no
surface no surface no surface flaw having flaws flaw flaw
Example 6
[0124] Coating 1 was coated on the PU foam obtained above by a roll
knife with wet thickness of 200 microns, then dried in an oven at
150.degree. C. for 2 minutes to form a skin layer. Coating 3 was
further coated on the skin layer with wet thickness of 60 microns,
then dried in an oven at 150.degree. C. for 1 minute to form an
finishing layer. The resultant multilayer structure was then cooled
down to ambient temperature for performance tests.
Comparative Example F Preparation of an Embossed Multilayer
Structure by Conventional Conditioning Direct Embossing
[0125] Coating 1 was coated on the PU foam obtained above by a roll
knife with wet thickness of 200 microns, then dried in an oven at
150.degree. C. oven for 2 minutes to form a dried skin layer.
Coating 3 was further coated on the dried skin layer with wet
thickness of 60 microns, then dried in an oven at 150.degree. C.
for 1 minute to form an finishing layer. The resultant sample was
then embossed using an ironing and embossing machine (Model:
GJ5D2-300 from Tianjin Leather Machninery Co. Ltd) under the
condition of 0.3 MPa, and 120.degree. C. for 40 seconds, wherein
the finishing layer was contacted with the roller. The resultant
multilayer structure was then cooled down to ambient temperature
for performance tests.
[0126] The multilayer structure of Example 6 had an adhesion
strength of around 1,250 g/cm and passed 10,000 times of bally flex
test. In addition, the multilayer structure of Example 6 showed
soft handfeel. In contrast, the embossed multilayer structure of
Comparative Example F failed the bally flex test at 45,000 times of
flexing, which also exhibited stiff handfeel. SEM images of the
multilayer structures of Example 6 and Comparative Example F are
shown in FIGS. 2 and 3, respectively. The foam in the multilayer
structure of Comparative Example F deformed severely compared to
that of Example 6. The foam thickness of the multilayer structure
of Example 6 was about 1200 microns as shown in FIG. 2. The foam
thickness of the multilayer structure of Comparative Example F was
about 650-750 microns as shown in FIG. 3.
* * * * *